Tumor cell infiltration causes the remodelling of peritumoral tissues, determined by an increased lytic activity of extracellular matrix exerted by the neoplastic invasive phenotype. Among the principal lytic enzymes produced by tumor cells and mainly involved in invasion process there are the matrix metalloproteases (MMPs). The Authors compared the plasmatic values of MMPs 2, 3, 9 from patients with breast carcinomas and fibroadenomas in order to evaluate whether there was a significant difference between the two groups of patients. MMPs 2, 3, 9 values were quantified by ELISA test from plasma collected 24 hours before surgery in 50 breast carcinomas and 30 fibroadenomas. MMP2 mean value from the patients with carcinomas resulted significantly higher as compared to that from the patients with fibroadenomas; while for MMP 3 and 9 mean values was not possible to find a significant difference between the two groups of malignant and benign breast tumors. These data confirm the main role played by MMPs during the tumor invasion process. Therefore, it is possible to propose the future inclusion of MMP2 test, together to other biological and clinical data, for prognostic evaluation of neoplastic breast lesions.